The present invention relates to a storage system and a snapshot creation method thereof.
Conventionally, a computer system that connects a host computer and a storage system with a network, and stores data processed with the host computer in the storage system by sending and receiving such data via the network has been put into practical application.
In this kind of computer system, remote copy technology is known for preventing the loss of data even when a disaster occurs in the storage system of a local site by configuring a volume group of the storage system of the local site and a volume group of the storage system of a remote site in a pair relationship for executing volume-to-volume copy, and copying (replicating) data from the volume group of the local site storage system to the volume group of the remote site storage system.
As background art related to remote copy technology, for instance, IBM REDBOOKS—Disaster Recovery with DB2 UDB for zOS; November 2004, and IBM REDBOOKS—The IBM Total Storage DS8000 Series: Copy Services with IBM Eserver zSeries; February 2006, disclose async remote copy technology for creating a backup of the volume group of the local site storage system in the volume group of the remote site storage system by periodically compiling and transferring the change difference of the volume group of the local site storage system asynchronously to the remote site storage system.
Nevertheless, with the foregoing async remote copy technology, upon transferring the change difference of the volume group of the local site storage system to the volume group of the remote site storage system, consistency regarding the writing sequence by the host computer in the volume or volume group of the local site storage system is not guaranteed.
Thus, with this async remote copy technology, when a disaster or the like occurs in the local site storage system during the transfer of data, such data may be damaged since the consistency of the volume group of the remote site storage system is not guaranteed.
Thus, also disclosed is remote copy technology which combines the async remote copy technology and the local copy technology in order to guarantee the existence of a volume with consistency regarding the writing sequence from the host computer in the remote site storage system at an arbitrary point in time. Specifically, with this remote copy technology, async remote copy is performed from a first volume group of the local site storage system to a second volume group of the remote site storage system, and, after transferring all change differences, local copy is performed from the second volume group to a fourth volume group of the remote site storage system. Like this, by alternately performing async remote copy and local copy, existence of a volume group having consistency will be guaranteed in the fourth volume group when transferring the change difference of the first volume group of the local site storage system to the second volume group of the remote site storage system.
Further, Using Asynchronous Replication for Business Continuity Between Two or More Sites; December 2004 discloses remote copy technology capable of configuring a volume group having consistency regarding the writing sequence from the host computer to the local site storage system even when a disaster or the like occurs in the local site storage system and subsequent data transfer cannot be performed by primarily storing difference data in a difference buffer in the remote site storage system.
Nevertheless, with the foregoing remote copy technology that combines async remote copy technology and local copy technology, when the second volume group and the fourth volume group are used for testing or the like in the remote site storage system during the system operation of the remote copy technology, it is necessary to discontinue the system operation in the remote copy technology until such testing is complete. Further, when data is written in the second volume group and the fourth volume group while such testing is being conducted, there is a possibility that such data cannot be backed up properly.
Thus, it is conceivable to newly prepare a third volume group in the remote site storage system and create a snapshot of the second volume group as the third volume group. Nevertheless, when creating a snapshot of the second volume group as the third volume group, there may be cases where the second volume group is copying the change difference, and, therefore, consistency of the writing sequence from the host computer in the local site storage system will not be guaranteed.
Here, in order to create a snapshot where the consistency is guaranteed, it is necessary to discontinue the system operation in the foregoing remote copy technology, issue a command to the local site for guaranteeing the consistency, create a snapshot of the second volume, and thereafter make the local site issue a command for resuming the system operation in the remote copy technology. Thus, complex operations such as the discontinuance and resumption of the system operation in the remote copy technology are required by the local site storage system, and will affect the system operation.
Moreover, even with the remote copy technology described in Non-Patent Document 3, when creating a snapshot of the second volume group in the remote site storage system during the system operation in the remote copy technology, there may be cases where the consistency is not guaranteed since it may be applying data of the difference buffer.